Fiberboard boxes have been made for many decades in several designs, the most usual consisting of a square or rectangular configuration having a flat top or bottom surface formed by four closure flaps. Precut slots or slits extending along a vertical edge of each flap separate each flap at each corner of the box to permit the flaps to be folded inwardly to close the top or bottom end of the box.
In applications where such boxes are used for containing a flowable bulk material, the usual slotted box configuration lacks strength around the horizontal score line between the bottom closure flaps and the vertical side walls which causes bulging of the side walls near this location. This is referred to as "elephant's foot" in the trade.
One attempted prior solution to this problem is represented in U.S. Pat. No. 3,523,635. This patent discloses a four-sided fiberboard box having a strengthened, corner and four flaps integrally joined along the horizontal score line forming the bottom edge of the box. Two of the opposed flaps are folded inwardly along diagonal score lines while the other two flaps are rectangular and fold inwardly toward one another. The flaps having the diagonal scored fold lines form a triangular shaped flap. This construction offered some improvement over the slotted box configuration because the bottom flaps are an integral extension of the side walls, however, this patent still teaches the need for an additional overlapping corner joint to strengthen the four sided box in order to provide an increase in strength over the slotted flap version.
When fiberboard boxes are used to contain flowable bulk materials in relatively large amounts which are stacked one upon the other, increased stacking strength and resistance to bulging of the side walls at or near the bottom is highly desirable. Some bulk bin box constructions have been proposed utilizing an equal sided octagon configuration in the form of a tube which requires a separate fitted top and bottom closure portion which are fixed to the tube by strapping, adhesive or staples, for example. Such constructions offer improved strength, however, at significantly increased costs of labor and at a significant decrease in volume per unit height compared to a conventional rectangular box configuration. Prior to the present invention a more economical box construction which provides increased strength in this regard without significant sacrifice of volume or storage space has eluded those skilled in the art.